Resistance to activated protein C as a basis for venous thrombosis

Pro- and anticoagulant properties of factor V in pathogenesis of thrombosis and bleeding disorders

Factor V (FV) serves an important role in the regulation of blood coagulation, having both pro- and anticoagulant properties. The circulating high molecular weight single-chain FV molecule undergoes a series of proteolytic cleavages during both activation of coagulation and during anticoagulant regulation of coagulation by activated protein C (APC). It is noteworthy that mutations in the factor V gene (F5) either cause thrombosis or bleeding. New insights into the importance and complexity of FV functions have been generated from elucidation of the pathogenic mechanisms of two familial mutations in the F5 gene. The first mutation was identified as a result of the discovery of APC resistance as the most common risk factor for venous thrombosis. The mutation (FV Leiden) predicts the Arg(506) Gln replacement, which impairs the normal regulation of FVa by APC, as the Arg506 site is an important APC cleavage site. In addition, elucidation of APC resistance resulted in the discovery of the anticoagulant APC cofactor activity of FV. The second FV mutation (FV(A2440G) ), identified in a family with an autosomal dominant bleeding disorder, has led to the discovery of an alternative splicing generating a previously unidentified FV isoform (FV-Short), which inhibits coagulation via an unexpected and intriguing mechanism involving the coagulation inhibitor TFPI-α. These are naturally occurring mutations in the F5 gene that have generated new knowledge on the role of FV in regulation of coagulation and the importance of genetic risk factors for thrombosis and bleeding.

Do incident and recurrent venous thromboembolism risks truly differ between heterozygous and homozygous Factor V Leiden carriers? A retrospective cohort study

INTRODUCTION

While Factor V Leiden (F5 rs6025 A allele) is a known venous thromboembolism (VTE) risk factor, VTE risk among heterozygous vs. homozygous carriers is uncertain.

MATERIALS AND METHODS

In a retrospective cohort study of Mayo Clinic patients referred for genotyping between 1996 and 2013, we tested Factor V Leiden genotype as a risk factor for incident and recurrent VTE.

RESULTS

Among heterozygous (n=268) and homozygous (n=111) carriers, the prevalence of VTE was 54% and 68%, respectively (p=0.016). While mean patient age at first VTE event (43.9 vs. 42.9years; p=0.70) did not differ significantly, median VTE-free survival was modestly shorter for homozygous carriers (56.8 vs 59.5 years; p=0.04). Sixty-nine (48%) and 31 (42%) heterozygous and homozygous carriers had ≥1 VTE recurrence (p=0.42). In a multivariable model, idiopathic incident VTE and a second thrombophilia were associated with increased and anticoagulation duration >6months with reduced hazards of VTE recurrence; Factor V Leiden genotype was not an independent predictor of recurrence.

CONCLUSIONS

Aside from a higher VTE prevalence and modestly reduced VTE-free survival, VTE penetrance and phenotype severity did not differ significantly among homozygous vs. heterozygous carriers, suggesting that VTE prophylaxis and management should not differ by Factor V Leiden genotype.

Factor V Leiden

Factor V Leiden (FVLeiden ) is a common hereditary thrombophilia that causes activated protein C (APC) resistance. This review describes many of the most fascinating features of FVLeiden , including background features, mechanisms of hypercoagulability, the founder mutation concept, the "FVLeiden paradox," synergistic interaction with other thrombotic risk factors, the intertwined relationship between FVLeiden and APC resistance testing, and other, uncommon mutations implicated in causing APC resistance. In addition, there are several conditions where laboratory tests for APC resistance and FVLeiden are or can be discrepant, including lupus anticoagulants, anticoagulants such as direct thrombin inhibitors (dabigatran, argatroban, and bivalirudin) and rivaroxaban, as well as pseudohomozygous, pseudo-wildtype, liver transplant, and bone marrow transplant patients. The laboratory test error rate for FVLeiden is also presented.

Combination of Surgical Thrombectomy and Direct Thrombolysis in Acute Abdomen with Portal and Superior Mesenteric Vein Thrombosis

Portal vein (PV) thrombosis (PVT) is a rare condition with development of thrombosis in the PV and its branches. Further extension to the splenic and superior mesenteric vein (SMV) causes intestinal infarction, with a reported mortality of up to 50%. A variety of treatments for PVT exist including anticoagulation, thrombolysis, surgical thrombectomy, insertion of shunts, bypass surgery, and liver transplantation. We experienced a case of successfully treated by surgical thrombectomy with direct thrombolysis into the thrombosed-PV and SMV. A 31-year-old male presented worsening abdominal pain for one week. Preoperative contrast enhanced computed tomography scan revealed complete PVT extending to splenic vein and SMV. The PV was accessed surgically and opened by thrombectomy; visual inspection confirmed proximal and distal flow. Urokinase was administered directly into the inferior mesenteric vein with successful decrease in thrombus burden. The complete angiography showed complete dissolution of thrombosis in PV and SMV.

Activated protein C resistance testing for factor V Leiden

Activated protein C resistance assays can detect factor V Leiden with high accuracy, depending on the method used. Factor Xa inhibitors such as rivaroxaban and direct thrombin inhibitors including dabigatran, argatroban, and bivalirudin can cause falsely normal results. Lupus anticoagulants can cause incorrect results in most current assays. Assays that include dilution into factor V-deficient plasma are needed to avoid interference from factor deficiencies or elevations, which can arise from a wide variety of conditions such as warfarin, liver dysfunction, or pregnancy. The pros and cons of the currently available assays are discussed.

Anticoagulant factor V: factors affecting the integration of novel scientific discoveries into the broader framework

Since its initial discovery in the 1940s, factor V has long been viewed as an important procoagulant protein in the coagulation cascade. However, in the later part of the 20th century, two different scientists proposed novel anticoagulant roles for factor V. Philip Majerus proposed the first anticoagulant function for factor V in 1983, yet ultimately it was not widely accepted by the broader scientific community. In contrast, Björn Dahlbäck proposed a different anticoagulant role for factor V in 1994. While this role was initially contested, it was ultimately accepted and integrated into the scientific framework. In this paper, I present a detailed historical account of these two anticoagulant discoveries and propose three key reasons why Dahlbäck's anticoagulant role for factor V was accepted whereas Majerus' proposed role was largely overlooked. Perhaps most importantly, Dahlbäck's proposed anticoagulant role was of great clinical interest because the discovery involved the study of an important subset of patients with thrombophilia. Soon after Dahlbäck's 1994 work, this patient population was shown to possess the factor V Leiden mutation. Also key in the ultimate acceptance of the second proposed anticoagulant role was the persistence of the scientist who made the discovery and the interest in and ability of others to replicate and reinforce this work. This analysis of two different yet similar discoveries sheds light on factors that play an important role in how new discoveries are incorporated into the existing scientific framework.

Endothelial Protein C Receptor Gene Variants and Risk of Thrombosis

Endothelial protein C receptor (EPCR) is a candidate mediator in the pathogenesis of thrombosis, as several data in the literature indicate that polymorphisms such as EPCR 4678G/C and 4600A/G are associated with either protective effect or increased risk of thrombosis, respectively. We investigated the prevalence of these polymorphisms in patients with thrombotic disorders as well as their impact on the risk of thrombosis, the age of first thrombotic episode, and recurrence. The prevalence of the rare EPCR alleles 4600G and 4678C was comparable in patients and controls. However, in a subset analysis, we observed that 4600G allele was more prevalent among patients who developed thrombosis at younger age (<35 years). Moreover, the prevalence of 4678C allele was significantly lower in younger patients compared to older patients. Neither polymorphism seemed to have an impact on recurrence regardless of age. Soluble EPCR levels were elevated in 4600AG patients compared to controls while 4678CC patients presented with lower levels of soluble form of EPCR compared to carriers of at least 1 4678G allele. Our data suggest that either the lack of the protective EPCR 4678C allele or the presence of EPCR 4600G allele may be associated with earlier development of thrombosis.

Factors that influence the bleeding phenotype in severe hemophilic patients

Hemophilia A and B are rare, X-linked bleeding disorders resulting from a partial or total deficiency of functionally active coagulation factor VIII or factor IX, respectively. Endogenous factor levels have traditionally been used to characterize the severity of the disorder, with severe hemophilia considered as circulating levels of factor less than 1% of normal. Identifying patients with severe hemophilia is essential to effective treatment, since these patients are at highest risk of spontaneous life or limb-threatening bleeding and disability resulting from repeated joint bleeding and are most likely to benefit from prophylaxis. However, there is variability in bleeding tendency, even among patients with severe hemophilia. This article will review potential modifiers of hemophilia-associated bleeding other than endogenous factor activity, which may influence bleeding tendencies and complications in hemophilic patients considered to have severe hemophilia. These potential modifiers include physiologic factors, such as elements of the hemostatic system; pathophysiologic factors, such as hemophilic arthropathy, associated inflammation, and angiogenesis; and others, such as seasonal variation, body weight, and physical activity.

Prevalence of hypercoagulable disorders in inflammatory bowel disease

OBJECTIVE. Inflammatory bowel disease (IBD) can be associated with hypercoagulable disorders. Aim of this single-center, prospective study was an in-depth evaluation of acquired hypercoagulable states in IBD patients. METHODS. A total of 110 patients with Crohn's disease (CD) (aged 19-69; mean 40.5, median 38.5 years), 43 with ulcerative colitis (UC) (aged 17-72; mean 42, median 36 years), and 30 controls were enrolled. Full blood count, serum C-reactive protein (CRP), proteins C and S, activated protein C (APC) resistance, thrombin-antithrombin complex (TAT), F1+F2 fragments, tissue factor pathway inhibitor (TFPI) total and truncated, TFPI-factor Xa, tissue plasminogen activator (tPA) and PAI-I antigen were investigated in peripheral blood samples. RESULTS. Only 18 of 153 (11.8%) IBD patients had hemocoagulation parameters within normal range. Significant difference between IBD patients and controls was found in thrombocyte volume (p < 0.001), protein C (p = 0.025), protein S (p = 0.003), APC resistance (p < 0.001), F1+F2 fragments (p < 0.001), and tPA (p = 0.002). In CD patients who were divided into two subgroups according to serum CRP values (non-active disease: <5 mg/L; active disease ≥5 mg/L), thrombocyte count was significantly lower (p = 0.001), thrombocyte volume was significantly higher (p = 0.002), F1+F2 fragments were significantly lower (p = 0.007) and tPA was significantly higher (p = 0.038) in the subgroup with CRP <5 mg/L. In UC patients, no significant difference depending on CRP was found. CONCLUSIONS. Acquired hypercoagulable abnormalities in IBD patients are frequent. Patients with active CD, but not UC, displayed significantly different hemocoagulable parameters, when compared to non-active CD/UC subjects. In patients with active CD (with increased serum CRP concentration) and patients with active extensive UC found at endoscopy (despite low CRP values), prophylactic anticoagulation therapy should be considered.

Inherited thrombophilia in children

Thrombosis in children has multiple etiologies, including inherited disorders such as factor V Leiden mutation, prothrombin 20210A mutation, and deficiencies in protein C, S, or antithrombin. Epidemiology of the disorders varies, as does the risk of thrombosis. Venous thromboembolism is the typical presentation. However, more severe anticoagulant protein deficiencies may present with purpura fulminans. Treatment of thrombosis is relatively uniform, regardless of the underlying genetic risk factor. In this article, we discuss the most well-studied inherited thrombophilias and the epidemiology, pathophysiology, and relative thrombotic risk of each. Treatment of thrombosis is also briefly reviewed.

Coagulation abnormalities in osteonecrosis and bone marrow edema syndrome

The aim of this review was to provide information about the variety of thrombophilic and hypofibrinolytic markers that are possible risk factors for the development of osteonecrosis and bone marrow edema syndrome. A total of 48 parameters were identified in 45 studies that included 2163 patients. The most frequently reported laboratory findings included altered serum concentrations of lipoproteins, decreased concentration and function of fibrinolytic agents, increased levels of thrombophilic markers, and several single nucleotide polymorphisms. Despite inhomogeneities in reported parameters, results, patients' collectives, and treatment strategies, these data suggest that coagulation abnormalities may play an important role in the emergence of osteonecrosis and bone marrow edema syndrome.

Ischemic bowel syndromes

Atherosclerotic vascular disease involving the mesenteric arteries occurs frequently in the elderly population. Although the prevalence of ischemic bowel disease is difficult to determine, acute mesenteric ischemia (AMI) has been reported to cause in 1 in 1000 hospital admissions, whereas chronic mesenteric ischemia (CMI) is estimated to affect 1 in 100,000 individuals. Mesenteric ischemia generally manifests in its chronic form as postprandial abdominal pain resulting in significant weight loss, and in its acute form as an abrupt development of abdominal pain, lower gastrointestinal bleeding, and subsequent intestinal necrosis. This article discusses the cause, clinical manifestations, diagnosis, and management of AMI and CMI.

Venous thrombosis and oral contraceptives: current status

The use of oral contraceptives is associated with an increased risk of venous thrombosis. It is now generally accepted that women who use oral contraceptives that contain so-called third-generation progestins (desogestrel or gestodene) are exposed to a twofold higher risk of venous thrombosis than women who use oral contraceptives that contain the second-generation progestin levonorgestrel. Coagulation studies demonstrated that oral contraceptives increase the plasma level of prothrombin, decrease the level of protein S and induce acquired activated protein C resistance. The changes in hemostatic parameters can explain why women who use oral contraceptives are exposed to an increased risk of venous thrombosis and why the risk is further increased in third-generation oral contraceptive users.

The prothrombotic phenotypes in familial protein C deficiency are differentiated by computational modeling of thrombin generation

The underlying cause of thrombosis in a large protein C (PC) deficient Vermont kindred appears to be multicausal and not explained by PC deficiency alone. We evaluated the contribution of coagulation factors to thrombin generation in this population utilizing a mathematical model that incorporates a mechanistic description of the PC pathway. Thrombin generation profiles for each individual were generated with and without the contribution of the PC pathway. Parameters that describe thrombin generation: maximum level (MaxL) and rate (MaxR), their respective times (TMaxL, TMaxR), area under the curve (AUC) and clotting time (CT) were examined in individuals ± PC mutation, ± prothrombin G20210A polymorphism and ± thrombosis history (DVT or PE). This family (n = 364) is shifted towards greater thrombin generation relative to the mean physiologic control. When this family was analyzed with the PC pathway, our results showed that: carriers of the PC mutation (n = 81) had higher MaxL and MaxR and greater AUC (all p<0.001) than non-carriers (n = 283); and individuals with a DVT and/or PE history (n = 13) had higher MaxL (p = 0.005) and greater AUC (p<0.001) than individuals without a thrombosis history (n = 351). These differences were further stratified by gender, with women in all categories generating more thrombin than males. These results show that all individuals within this family with or without PC deficiency have an increased baseline procoagulant potential reflective of increased thrombin generation. In addition, variations within the plasma composition of each individual can further segregate out increased procoagulant phenotypes, with gender-associated plasma compositional differences playing a large role.

The role of hypercoagulability in the development of osteonecrosis of the femoral head

Despite the large number of the outstanding researches, pathogenesis of osteonecrosis remains unknown. During the last decades the hypothesis that increased intravascular coagulation may be the pathogenetic mechanism which leads to osteonecrosis is gaining constantly support. Both primary factors of hyper-coagulability, such as resistance to activated protein C, protein C and protein S deficiency, low levels of tissue plasminogen activator, high levels of plasminogen activator inhibitor, von Willebrand factor, lipoprotein (a), and secondary factors of hypercoagulability with factors potentially activating intravascular coagulation, such as pregnancy, antiphospholipid antibodies, systemic lupus erythematosus, hemoglobinopathies and sickle cell disease, and hemato-oncologic diseases are discussed in this article. Although coagulation abnormalities in patients with hip osteonecrosis might represent increased risk factors for the development of bone necrosis by predisposing the patient to thromboembolic phenomena, further investigation is needed to indicate the definite correlation between factors leading to increased intravascular coagulation and pathogenesis of osteonecrosis.

Thrombophilic screening in Turner syndrome

AIM

The aim of this study was to determine, in patients with Turner syndrome (TS), the prevalence of thrombophilic disorders correlating with a higher risk of venous thromboembolism (VTE), to evaluate if thrombophilia is associated with the genetic features of these patients and whether screening before hormone replacement therapy (HRT) is advisable.

PATIENTS AND METHODS

We examined 82 TS patients. In all patients we analyzed activated factor VIII:C, fibrinogen, antithrombin (AT), protein C (PC), protein S (PS), activated PC resistance, and homocysteine. For every patient, an investigation for mutations in prothrombin G20210A, factor V R506Q, methylenetetrahydropholate reductase (MTHFR) C 677T and A1298C was conducted.

RESULTS

Low values of PC in 3 patients (3.70%), low values of PS in 12 (14.81%), and hyperhomocysteinemia in 4 (4.87%) were found; 52 girls (64.2%) presented hyperfibrinogenemia. Three patients were heterozygous for the prothrombin G20210A allele mutation (3.66%) and the factor V mutation was present in 4 patients (4.88%). No TS patient had a homozygous mutation. Mutations in the MTHFR gene were present in 62 girls, in 17 patients (20.7%) they were homozygous and in 45 patients (54.88%) heterozygous.

CONCLUSIONS

Considering the increased risks with the association between VTE and the higher prevalence of PC and PS deficiencies, TT genotype mutations and high level of fibrinogen, it is advisable to perform a complete thrombophilia screening in TS patients before starting HRT.

Thrombophilia Due to Factor V and Factor II Mutations and Formation of a Dural Arteriovenous Fistula: Case Report and Review of a Rare Entity

Genetic mutations underlying thrombophilia are often recognized in patients with thromboembolic episodes. However, the clinical and therapeutic implications of such findings often remain unclear. We report the first case of a dural arteriovenous fistula (DAVF) in a patient with a combined factor II and factor V Leiden mutation. A 40-year-old man presented with a large left temporal and intraventricular hemorrhage. An initial angiogram showed thrombosis of the left sigmoid sinus but no evidence of a vascular malformation. One year after the hemorrhage, an angiographic study showed the appearance of a right DAVF. During the follow-up period, the patient was found to harbor heterozygosity for a mutation of factor V and a mutation of factor II. Recognition of the patient's thrombophilia led to prolonged oral anticoagulation therapy to reduce the risk of a recurrent thrombotic episode. Despite the increased risk of bleeding, the therapy was considered justified. DAVFs may occur after sinus thrombosis in patients with combined factor II and factor V mutations. This observation indicates the association of multiple hematological disorders with DAVFs in individual patients. Moreover, it raises the clinical conundrum of how to manage patients with thrombophilia, intracranial hemorrhage, and DAVFs.

Cerebral sinovenous thrombosis associated with factor V Leiden and methylenetetrahydrofolate reductase A1298C mutation in adult membranous glomerulonephritis

Thromboembolic diseases are accepted as the most important complications in adult nephrotic syndrome, particularly membranous nephropathy. As renal vein thrombosis is usually seen in patients with membranous nephropathy, cerebral venous thrombosis is a very rare condition, which has not been reported previously in adult patients with membranous nephropathy. Although acquired dysfunctions of coagulation and fibrinolytic systems are responsible for hypercoagulopathy in patients with nephrotic syndrome, the two most common causes of hereditary venous thrombosis [the mutations of factor V Leiden and methylenetetrahydrofolate reductase (MTHFR)] facilitate thrombosis in arterial and venous system in these patients. We report a 56-year-old man with sinovenous thrombosis, diagnosed as membranous nephropathy and detected to have mutations in factor V Leiden and MTHFR A1298C. Our patient is important because he had genetic risk of thrombotic conditions and was the first adult patient with membranous nephropathy.

Hematologic genetic testing in high-risk patients before knee arthroplasty: a pilot study

BACKGROUND

Patients with a personal or familial history of thromboembolism are considered at higher risk for thromboembolic disease after knee arthroplasty. While it remains unclear why some patients develop deep vein thrombosis (DVT) or pulmonary embolism (PE) despite similar operative procedures and the same prophylactic regimen, we presume one explanation would be genetic predisposition.

QUESTIONS/PURPOSES

We determined the frequency of 12 factors including antithrombin III activity, prothrombin gene mutations, and the presence of phospholipid antibodies in a high-risk patient cohort and compared those findings with the known prevalence in the population at large.

PATIENTS AND METHODS

Patients identified preoperatively as having a personal or familial history of DVT and/or PE were referred for hemostatic serum and genetic tests, including % antithrombin III activity (ATIII), protein C and protein S activities, APC resistance, Factor V gene (Leiden) mutations, prothrombin gene mutations, lupus anticoagulant antibody presence, cardiolipin antibody presence, phosphatidyl antibody presence, β2-glycoprotein antibody presence, and serum homocysteine and lipoprotein(a) levels The frequencies of varying abnormalities were identified and compared to the prevalence reported in the literature.

RESULTS

Forty-three of 1944 patients undergoing knee arthroplasty had a history of DVT or PE. Sixteen of 43 (37%) patients had an abnormality and eight of these (19%) had two or more abnormalities. The frequency of nine of the 12 tests appeared to be greater in this cohort than in the population at large.

CONCLUSIONS

Patients with a personal or familial history of DVT or PE appear to have a high frequency of hereditary prothrombotic abnormalities. Preoperative evaluation by a hematologist may be warranted in patients with a personal or familial history of DVT or PE as the postoperative anticoagulation protocols may be altered and identification of these abnormalities may affect a patient's risk for other disease states.

LEVEL OF EVIDENCE

Level IV, diagnostic study. See Guidelines for Authors for a complete description of levels of evidence.

Speaking the Language of Genetics: A Primer

Genetic research advances will continue to result in clinical applications for genetics in primary care settings. Fluency with the evolving genetic terminology will enable primary care providers to provide better clinical care to their patients, particularly when helping patients understand genetic concepts. This article will help clinicians use genetic terminology with greater precision.

Factor V Leiden and FII 20210 testing in thromboembolic disorders

Factor V Leiden and prothrombin (F2) c.20210G>A mutation detection are very important in order to define the increased relative risk for venous thromboembolism in selected patients. Use of DNA-based methods to detect both mutations has become widely available in clinical diagnostic laboratories, including fluorescence-based quantitative real-time PCR (qPCR). The latter is a rapid, simple, robust and reliable method to identify genotypes of interest. There are several chemistries used for qPCR; this article describes their principles and applicability for Factor V Leiden and prothrombin (F2) c.20210G>A mutation detection.

Guidelines for the prevention of stroke in patients with stroke or transient ischemic attack: a guideline for healthcare professionals from the american heart association/american stroke association

The aim of this updated statement is to provide comprehensive and timely evidence-based recommendations on the prevention of ischemic stroke among survivors of ischemic stroke or transient ischemic attack. Evidence-based recommendations are included for the control of risk factors, interventional approaches for atherosclerotic disease, antithrombotic treatments for cardioembolism, and the use of antiplatelet agents for noncardioembolic stroke. Further recommendations are provided for the prevention of recurrent stroke in a variety of other specific circumstances, including arterial dissections; patent foramen ovale; hyperhomocysteinemia; hypercoagulable states; sickle cell disease; cerebral venous sinus thrombosis; stroke among women, particularly with regard to pregnancy and the use of postmenopausal hormones; the use of anticoagulation after cerebral hemorrhage; and special approaches to the implementation of guidelines and their use in high-risk populations.

Factor V Leiden mutation and thromboembolism risk in women receiving adjuvant tamoxifen for breast cancer

BACKGROUND

Tamoxifen use has been associated with increased risk of thromboembolic events (TEs) in women with breast cancer and women at high risk for the disease. Factor V Leiden (FVL) is the most common inherited clotting factor mutation and also confers increased thrombosis risk. We investigated whether FVL was associated with TE risk in women with early-stage breast cancer who took adjuvant tamoxifen.

METHODS

A case-control study was conducted among 34 Cancer and Leukemia Group B (CALGB) institutions. We matched each of 124 women who had experienced a documented TE while taking adjuvant tamoxifen for breast cancer (but who were not necessarily on a CALGB treatment trial) to two control subjects (women who took adjuvant tamoxifen but did not experience TE) by age at diagnosis (+/-5 years). DNA from blood was analyzed for FVL mutations. Conditional logistic regression was used to estimate odds ratios (ORs) and to evaluate other potential factors associated with TE and tamoxifen use. All P values are based on two-sided tests.

RESULTS

FVL mutations were identified in 23 (18.5%) case and 12 (4.8%) control subjects (OR = 4.66, 95% confidence interval = 2.14 to 10.14, P < .001). In the multivariable model, FVL mutation was associated with TE (OR = 4.73, 95% confidence interval = 2.10 to 10.68, P < .001). Other statistically significant factors associated with TE risk were personal history of TE and smoking.

CONCLUSIONS

Among women taking adjuvant tamoxifen for early-stage breast cancer, those who had a TE were nearly five times more likely to carry a FVL mutation than those who did not have a TE. Postmenopausal women should be evaluated for the FVL mutation before prescription of adjuvant tamoxifen if a positive test would alter therapeutic decision making.

Comparison of characteristics from White- and Black-Americans with venous thromboembolism: a cross-sectional study

When compared with Whites, Black-Americans may have a 40% higher incidence venous thromboembolism (VTE) incidence. However, whether other VTE characteristics and risk factors vary by race is uncertain. To compare demographic and baseline characteristics among White- and Black-Americans with VTE, we used data prospectively collected from consecutive consenting adults enrolled in seven Centers for Disease Control (CDC) Thrombosis and Hemostasis Centers from August 2003 to March 2009. These characteristics were compared among Whites (n = 2002) and Blacks (n = 395) with objectively diagnosed VTE, both overall, and by age and gender. When compared with Whites, Blacks had a significantly higher proportion with pulmonary embolism (PE), including idiopathic PE among Black women, and a significantly higher proportion of Blacks were women. Blacks had a significantly higher mean BMI and a significantly lower proportion with recent surgery, trauma or infection, family history of VTE, and documented thrombophilia (solely from reduced factor V Leiden and prothrombin G20210A prevalence). Conversely, Blacks had a significantly higher proportion with hypertension, diabetes mellitus, chronic renal disease and dialysis, HIV, and sickle cell disease. When compared with White women, Black women had a significantly lower proportion with recent oral contraceptive use or hormone therapy. We conclude that Whites and Blacks differ significantly regarding demographic and baseline characteristics that may be risk factors for VTE. The prevalence of transient VTE risk factors and idiopathic VTE among Blacks appears to be lower and higher, respectively, suggesting that heritability may be important in the etiology of VTE among Black-Americans.

Factor V Leiden and the risk of venous thrombosis, myocardial infarction, and stroke: a case-control study in Venezuela

The most common genetic defect associated with deep vein thrombosis (DVT) is a mutation in the Factor V gene (G1691A), known as Factor V Leiden (FVL). We investigated the genotypes for FVL in 571 individuals in Venezuela: 208 patients with DVT, 175 patients with acute myocardial infarction, 54 patients with stroke, and 134 control subjects. Our results showed in the population analyzed here that the FVL was associated with a fourfold increase in the risk for DVT (odds ratio, 4.24; 95% confidence interval, 1.35-14.79); particularly, women carriers showed a 6.5-fold increase in the risk for DVT. No relation was observed between the presence of FVL and the risk for acute myocardial infarction or stroke. In conclusion, a clear association between the FVL mutation and DVT was observed in the population analyzed in Venezuela. These results are in agreement with those found in other populations with different ethnic backgrounds.

Increased risk of venous thrombosis by AB alleles of the ABO blood group and Factor V Leiden in a Brazilian population

Most cases of a predisposition to venous thrombosis are caused by resistance to activated protein C, associated in 95% of cases with the Factor V Leiden allele (FVL or R506Q). Several recent studies report a further increased risk of thrombosis by an association between the AB alleles of the ABO blood group and Factor V Leiden. The present study investigated this association with deep vein thrombosis (DVT) in individuals treated at the Hemocentro de Pernambuco in northeastern Brazil. A case-control comparison showed a significant risk of thrombosis in the presence of Factor V Leiden (OR = 10.1), which was approximately doubled when the AB alleles of the ABO blood group were present as well (OR = 22.3). These results confirm that the increased risk of deep vein thrombosis in the combined presence of AB alleles and Factor V Leiden is also applicable to the Brazilian population suggesting that ABO blood group typing should be routinely added to FVL in studies involving thrombosis.

Analysis of endothelial protein C receptor functionality on living cells'

Activated protein C (APC) is a major control system of blood coagulation. APC prevents coagulation pathway by degrading Va and VIIIa plasma's coagulation factors. Protein C activation requires its binding to specific endothelial cell receptor (EPCR). APC binding to EPCR also activates a wide range of defense mechanisms (anti-inflammatory, antiapoptosis...). EPCR expression by cells can be detected by various methods, including immunoanalysis and molecular biology. However, no assays evaluate its functionality. A method, inspired of a standard fibrinoformation time assay, was developed to estimate EPCR ability to bind APC on living cell surface in vitro. Endothelial cells were incubated with APC and fibrinoformation on cells was followed by spectrophotometry (plasma absorbance increases with fibrin polymerization). Membrane-bound EPCR retain APC, thus prolonging fibrinoformation time in a dose-dependent manner. Control was realized with EPCR-negative cells. This new method can be used on any cell type to study the expression of other coagulation receptors.

Incidence of and risk factors for childhood thrombosis: a single-center experience in Ankara, Turkey

This study was conducted to analyze the incidence of and risk for thrombosis in thrombotic children monitored in the Department of Pediatric Hematology of our hospital at the time of diagnosis, in addition to the clinical characteristics of those patients. The clinical and laboratory findings of 122 patients diagnosed with thrombosis from 1997 to 2006 were retrospectively analyzed. The incidence of thrombosis was 88.6/10,000 hospital admissions. The authors found that 31.1% of the patients studied had a thrombosis in more than 1 region. The incidence of thrombosis by anatomic site was as follows: 42 thromboses in the peripheral arterial system, 39 in an intracardiac region, 38 in the abdominal venous system, 36 in the deep peripheral venous system, and 28 in the cerebral vascular system. The mean age of the patients at the time of diagnosis was 4.9 years. Of the patients studied, 10.7% were neonates, 35.3% were infants younger than 1 year, and 48.4% were younger than 2 years. Most of the patients had a congenital cardiac disease and spontaneous thrombosis, and 66.1% had at least 1 acquired risk factor, the most common of which were having undergone surgery (42%) or wearing a central venous catheter (39%). A hereditary factor for the development of thrombosis was present in 54% of the patients. The most frequently observed hereditary risk factor was the MTHFR 677C-T mutation, and the second most common was the factor V Leiden mutation. Thrombosis should be considered a systemic disorder, and thrombotic patients should be evaluated with appropriate methods. Acquired and hereditary risk factors should be analyzed systematically in thrombotic patients.

The Factor V Leiden mutation is associated with a higher blood haemoglobin concentration in women below 50 of the Malmö Thrombophilia Study (MATS)

The aim of this study was to investigate a relationship between FVL-mutation and levels of haemoglobin (Hb) in patients with venous thromboembolism (VTE). From March 1998 to December 2005, 927 consecutive patients with objectively diagnosed VTE were registered in the Malmö Thrombophilia Study (MATS). Female patients with FVL-mutation below 50 years of age had significantly higher median-Hb (133 vs. 126 g/l; P < 0.001) compared to female patients below the age of 50 years without FVL. No significant difference could be found for men or women above 50 years of age or men below 50 years of age. Female patients below the age of 50 years with FVL-mutation and VTE are associated with higher median Hb, and this finding is in accordance with earlier hypothesis that FVL-mutation may have constituted an evolutionary selection advantage.